Radio receiving apparatus



July 31, 1934.

| L. DE KRAMOLIN 1,963,335

RADIO RECEIVING APPARATUS Filed NOV. 28. 1928 Fig. 1.

Fig. 2.

,b A Wa ve/2 new;

1,968,335 nAnro aucnrvruc APPARATUS Leon Ladislas dc Kramolin, Berlin-Pankow,

' Germany Application November 28, 1928, Serial No. 322 126 In Germany December 1, 1927 2 Claims. (CL 250-20) The invention relates to improved apparatus and circuit arrangements for radio receivers and has for its object to simplify the control without spoiling other properties which it is desirable that a radio receiver should possess.

In'the superheterodyne system of radio reception, as at present known, it is necessary to employ two tuning elements, one in the entry circuit which receives the oscillations from the ether and the other in the localoscillation circuit.

The duty of the en try circuit is to select the station from which it is desired to receive signals as well as to increase nals to be received to the amplitude of the sigthe highest possible value.

The dutyof the local oscillation circuit is to maintain local oscillations which are combined with the received oscillations to yield an intermediate frequency suitable for amplification in vacuum tube amplifiers. In receivers where a single adjustable element is employed to control the tuning of the entry circuit and the tuning of the oscillation circuit, there is a problem of matching the condensers termediate frequency in the two circuits so that the inwill remain constant over the tuning range of the receiver, and there is also a further problem of accurately connecting the tuning condensers to the commonadjustable element.

An object of the present invention is to provide a superheterodyne radio receiver wherein satisfactory control by a single adjustable element is possible.

A further object of the invention is to provide a radio receiver controlled by a single adjustable element, wherein the necessity for accurately made condensers and accurate gauging between adjustable tuning elements is eliminated.

Still another object ate the possibility of of the invention is to obviinterference between incoming waves in a radio receiver controlled by a single adjustable devic ing range with substantially uniform amplitude,

and simultaneously controlling the tuning of the band pass filter with the tuning of the local oscillation generator. The by the filter is made small band of frequencies passed and sufiiciently wide to always include at least one carrier frequency which when combined with the local oscillator frequency produces th e desired intermediate frequency to which the intermediate frequency amplifier is tuned. The passed band is sufficiently narrow to exclude the image frequency carrier, that is, the carrier located on the opposite side of the oscillator frequency from the desired frequency.

The invention is illustrated in the accompanying drawing wherein: i

Figure 1 is a circuit diagram of a receiver embodying the invention.

Figure 2 is the resonance curve of the filter arrangement shown in the input circuitof the arrangement illustrated in Figure 1.

Referring to Figure 1, the oscillations picked up by the aerial 1 are conveyed through a filter system A, to be described further below, and applied to the grid 2 of an amplifier tube B. The anode circuit of this tube is inductively coupled through transformer 11 with the entry circuit of the oscillator tube C which also serves as a detector. In order to obtain a proportional amplification of the impulses, it may be desirable to allow the oscillatory circuit to work with anode bend or commutator effect instead of detector or modulation effect. The intermediate frequency received here is then amplified further in the tubes D and E which constitute a Kramolin high frequency amplifier as described in the specification of my German application K106659 VIII 2la2, The circuit of this amplifier is distinguished by great separating sharpness and sensitivity. The output circuit of tube E is connected to any suitable detector and reproducing device.

The filter A in the aerial circuit comprises the series connected variable condensers 3 and 4, and the shunt connected inductances 5, 6 and 7. The frequency responsive characteristic of such an arrangement is shown in Fig. 2, from which it can be seen that over a band of carrier frequencies ab, the response is substantially uniform, it falling off rapidly on either side of the frequencies a and b. The position of the frequency range a-b in the wave spectrum can be varied by adjustment of the condensers 3 and i which may be mechanically coupled together. In this manner the input circuit may be adjusted so that the desired incoming carrier frequency is included within the range a-b.

As' is well-known in normal superheterodyne receivers, on any particular adjustment, two transmitters can be heard at the same time, since with each frequency of oscillation of the oscillator, two different receiving waves, one above and one below the oscillation frequency, yield the same intermediate frequency. In normal receivers the possibility of disturbance, however, on account of the tuned pick-up circuit, is rather limited. In the case of the present invention, where the first tuning circuit comprises a band pass filter, said filter is designed to pass a band of frequencies such that possible interfering waves such as the image waves lie outside the band of frequencies a-b passed by the filter.

If by way of example the wireless range of about 200-550 meters is to be received, then a wave of 600 meters which equals 500,000 oscillations per second is chosen as intermediate frequency. The oscillatory circuit would then have to produce a variable wave between 2,000,000 and 1,045,000 oscillations per second to enable the range mentioned to be received. Waves, the length of which. do not come within the ordinary radio-telephony waveband, but are still able to produce the necessary intermediate frequency of 500,000 vibrations per second, then lie between 120 and 193.5 meters and therefore outside the range of reception. The local oscillations are generated in the tube C by back coupling between the inductance 8, connected in the anode circuit and the inductance 9 in the grid circuit thereof. The frequency of the oscillations generated is varied by means of the variable tuning condenser 10 connected in shunt with the inductance 9. For the purpose of obtaining single knob control as is the object of the invention, a mechanical coupling 12 is provided between the condenser 10, and the tuning condensers 3 and 4 of the filter circuit A. At the first glance, it appears as though this arrangement has no advantage over the wellknown tuned entry circuit, since there are really present two tuning circuits which must be coupled with one another to be manipulated, before oneknob manipulation is possible. However, when using a tuned entry circuit, its tuning must be kept exact, while in the arrangement illustrated,

with only approximate adjustment using a precalculated form of condenser plate made according to factory conditions with moderate accuracy, the summit of the resonance curve of the main tuning circuit for the desired frequency can be made to be included in the range of high amplitude in the entry circuit. The difference between the two wave lengths a and b indicates the possible range within which the tuning of the entry circuit can be varied simultaneously with the tuning of the oscillator circuit without losing the advantage of resonance amplification in the pick-up circuit.

I claim:

1. In a radio system for receiving a predetermined range of carrier frequencies, the combination of an input circuit including a tunable filter network for passing a narrow band of said carrier frequencies with substantially equal facility within said receiving range, means for variably tuning said network to shift said passed band over said receiving range of frequencies, a local oscillator circuit, means for varying the frequency of said oscillator circuit, a mechanical connection between said filter tuning means and said oscillator tuning means for simultaneously adjusting the tuning of said filter network and the frequency of said oscillator circuit such that the frequency of the oscillator differs from a desired frequency lying within said passed band by a fixed frequency difference, means for combining the oscillations of said passed band with the oscillations of said local oscillator circuit to produce a band of beat frequency oscillations, and an output circuit tuned to pass oscillations of a beat frequency corresponding to said fixed difference frequency.

2. In a radio system for receiving a predetermined range of carrier frequencies, the combination of an input circuit including a tun-able filter network for passing a narrowband of said carrier frequencies with substantially equal facility within said receiving range, means for variably tuning said network to shift said passed band over said receiving range of frequencies, a local oscillator circuit, means for varying the frequency,

.110 between said filter tuning means and said oscilof said oscillator circuit, a mechanical connection lator tuning means for simultaneously adjusting the tuning of said filter network and the -fre-.

quency of said oscillator circuit such that the frequency of the oscillator diifers from a desired frequency lying within said passed band by a fixed frequency difference, means for combining the oscillations of said passed band with the oscillations of said local oscillator circuit to produce a band of beat frequency oscillations, and an output circuit tuned to pass oscillations of a beat frequency corresponding to said fixed difference frequency, the arrangement being such that the band filter excludes the image carrier frequency.

LEON LADISLAS DE KRAMOLIN. 

